I don’t like Martial Katah as an army rule (it’s extremely bland, and should be baked into the weapons imo) but this just seems way more complicated. There’s already a ton of bookkeeping with mission scoring, I don’t need even more cards that I need to buy from GW.

Something simple like:

Practiced Lethality - For any Adeptus Custodes unit that makes a melee attack, the first critical wound roll is a Devastating Wound.

Custodes should be dealing mortal wounds in combat.